I don't want to argue semantics, but I would say it is an expressive action which is protected. A call to action, like yelling "fire" or something similar is different.
I think the opinion piece in the Johnson case sums it up quite nicely.
“If there is a bedrock principle underlying the...
Burning the flag is protected speech. A disgraceful act for sure, but protected none the less. Making this act a felony weakens freedom of speech and creates a slippery slope moving forward.